1. Field of the Invention
The present invention relates to an external fixator for use in orthopedic surgical applications, and more particularly to a method and apparatus for external fixation of an ankle.
2. Discussion of the Related Art
In various orthopedic surgical procedures, it is necessary to secure two bone portions in a relatively fixed relationship to each other. For example, the need for establishing such a secured relationship is often a result of a fracture which has occurred to the bone. To ensure that the bone can regenerate in the proper orientation and fuse the fracture, it is important that the bone portions be fixed and in the desired position during bone regeneration.
Various external fixation devices for the repair of traumatized bone are known. For example, U.S. Pat. No. 5,662,650 to Bailey et al. discloses an apparatus for the external fixation of large bones. The apparatus is illustrated to include a main body as well as a first and second bone screw clamps. The main body serves to allow the apparatus to axially rotate, thereby providing a proper longitudinal rotational location of the bone screws with respect to a bone. The first bone screw clamp is used to secure a first bone screw to the apparatus while permitting the first bone screw to be axially displaced from the main body. In a similar fashion, the second bone screw clamp functions to secure a second bone screw to the apparatus and to allow the second bone screw to be axially displaced with respect to the main body. U.S. Pat. No. 5,662,650 is incorporated by reference as if fully set forth herein.
In certain orthopedic surgical procedures, it is necessary to employ an external fixation device for immobilizing or restricting motion of the ankle joint. One known external fixator for an ankle joint is a monolateral cross-ankle articulated fixator manufactured by Orthofix SRL. This fixator is intended to allow motion at the ankle joint as a fracture heals. The fixator is applied with two pins distally, one in the talus and one in the calcaneus, and two pins proximally in the tibia. A distal clamp is attached to a body of the fixator by a uniaxial hinge that is centered over the medial side of the talus. The hinge axis is aligned along the horizontal ankle axis. The hinge is released post-operatively so that the patient may perform passive and active motion.
While known external fixators specifically designed for supporting an ankle joint may have proven to be acceptable for certain applications, such fixators are nevertheless susceptible to improvements that may enhance their performance. In this regard, the hinge position for known external fixators is established by insertion of talar and calcanear pins, thereby requiring pin positioning to accommodate hinge adjustment. Additionally, the clamps of known ankle fixators force the calcanear and talar pins to be parallel. This is true even if the calcanear and talar pins are not inserted exactly parallel. Furthermore, radiographic examination of the ankle joint is typically hindered by conventional ankle fixators since the anatomical pivot axis of the human ankle joint is aligned with structure defining a pivot axis of the fixator.